The invention relates to a method for controlling an electrical power steering system and to an electrical power steering system for implementing the method.
U.S. Pat. No. 6,425,454 B1 describes an electrical power steering system and a method for operating the electrical power steering system, in which the steering moment applied by a driver of a vehicle to a steering handle to change the steering angle adjustment of one or more steered wheels of the vehicle is transferred by way of a steering shaft. To support the steering force of the driver, an electrical servomotor is provided, in which a motor-regulating moment is generated at the steering handle, as a function of the steering angle reference value and a steering moment entered in a control and/or regulation device at the steering handle,. The motor-regulating moment is transferred to the steering shaft and to the steered wheel or the steered wheel or wheels by way of a power take-off. The electrical power steering has a sensor mechanism, consisting of an angle sensor and a moment sensor at the steering handle, and, among other things, an angle sensor to measure the angle of rotation of the power take-off of the electrical servomotor. A torque sensor to measure the torque at the power take-off of the electrical servomotor is not necessary, since the electrical power steering system has a device for estimating the moment at the steering handle and for estimating the moment at the power take-off of the electrical servomotor.
Using the sensor signals, such an electrical power steering can be controlled as a function of the construction of the electrical servomotor, for example by way of a field-oriented control system, the angle of rotation of the power take-off of the electrical servomotor being detected by the sensors, as a function of the movement of the steering handle and supplied to the control and/or regulation device, and the servomotor being controlled by way of the current frequency or the electrical power supplied, actual travel and vehicle parameters preferably being taken into consideration.
If an error or a failure occurs at the moment sensor at the steering handle with such electrical power steering mechanisms, the electrical servomotor is switched off; depending on the driving situation in each instance, this can result in a great increase in the moment to be applied by the driver at the steering handle, and can result in irritation of the driver.